1. Field of the Invention
This invention relates to a mold for continuously casting slabs, billets and related products which have a basically quadrangular, normally rectangular, cross section. The operation of a continuous casting machine with a mold such as provided by this invention, involves charging a casting mold with liquid metal and precooling the metal in the mold for the purpose of forming a strand having a closed shell of solidified metal surrounding a still liquid core, with the strand leaving the mold and being supported after it has left the mold, at least on the opposite wide sides by means of support or guide rolls, as shown in my U.S. Pat. No. 3,710,847 of Jan. 16, 1973.
2. Description of the Prior Art
It is known to those familiar with this technology, and disclosed in my prior patents U.S. Pat. No. 3,589,429 of June 29, 1971 and U.S. Pat. No. 3,710,847 of Jan. 16, 1973, that a strand with only a relatively thin shell of solidified metal is formed in the mold of continuous casting plants. Complete solidification of the strand occurs in the so-called secondary cooling zone after leaving the mold. The strand shell formed in the mold, due to its relative thin walls and also due to the high temperature, is not able to resist the ferrostatic pressure of the liquid strand core enclosed by the shell. Therefore, supporting devices such as rolls, plates, lifting beams and similar devices have to be provided which prevent excessive bulging or tearing of the shell. The supporting devices provided have to be adjusted to accommodate the size of the strand being cast and must be precisely aligned with the mold which results in considerable adjusting and alignment work, especially for facilities which change cast sizes frequently. Also affected by frequent size changes is the total production rate of machines due to the interruptions in operating availability. The supporting devices may be damaged considerably during breakouts of the strand leaving the mold which causes additional repair costs.
Normally the rectangular cross section of the strand leaving the mold is determined by the shape of the exit cross section of the mold. For so-called slow casters and for continuous casting machines for strands with relatively small thickness, it is satisfactory sometimes to support the strand leaving the mold only on the wide sides, although small bulges due to the ferrostatic pressure may occur on the small sides. These small bulges may be acceptable in certain special cases.
For larger strand thicknesses as in the case of thick slabs, and also for so-called high speed casters as well as for essentially square strands, supporting devices are also necessary for the other two sides of the strand, that is for the narrow sides in the case of a rectangular format as shown in U.S. Pat. No. 1,841,297 of Jan. 12, 1932 and U.S. Pat. No. 3,318,366 of May 9, 1967. Otherwise these sides of the strand would bulge excessively due to the ferrostatic pressure and cause danger of breakouts. The adjustment and alignment of the rolls supporting the narrow sides must also be provided for since changing of strand width is much more common than changing of strand thickness.
Molds for casting strands having several cross sectional configurations, including molds with internal walls that are concave surfaces, are shown in the aforesaid U.S. Pat. No. 1,841,297 of Jan. 12, 1932, and U.S. Pat. No. 3,075,264 of Jan. 29, 1963.